The present invention relates generally to equipment used for automating repetitive product manufacturing and assembly operations. More specifically, thus invention pertains to a modular indexing chassis for use in a pallet-type manufacturing process line.
In high-speed manufacturing and assembly systems, parts or components (sometimes generally referred to as xe2x80x9cworkpiecesxe2x80x9d) are typically transported along a conveyor-type assembly line by means of a small movable platform, known as a pallet. The pallet is stopped at various locations along the assembly line so that some type of assembly operation can be performed. In a typical assembly line installation, the pallets are placed on moving belts on a conveyor.
Conventional pallet conveyors in a manufacturing process line generally operate in either a synchronous or asynchronous mode. In synchronous systems, the conveyor is intermittently driven to move the pallets between workstations. The workpieces are transported by the pallets that ride on top of the conveyor. The workpiece and pallet proceed through each stage of the assembly process but do not move to the next workstation until all of the workpieces are also ready to proceed, i.e., each workpiece is synchronized with the other workpieces. Thus, in synchronous assembly systems, the conveyor stops after each workpiece arrives at its respective workstation and the stage or task that takes the greatest amount of time will limit the rate at which all other tasks or stages can be completed. Synchronous pallet conveyors can be relatively simple to make and use because the pallets are typically frictionally conveyed, no stop device is typically used, and the pallets are generally not disengaged from the conveyor at the workstations. However, the throughput speed of the conveyor line is limited to the throughput speed of the slowest workstation.
In non-synchronous assembly systems, the conveyor is continuously moving forward. Multiple slower tasks can be performed concurrently by employing combinations of divide modules or divide sections. At a divide section, pallets are diverted from the main conveyor to spur conveyors so that the slow task may be performed on a number of workpieces at the same time. Divide sections are designed to send workpieces with the slowest task completed down the conveyor at the line rate or the rate at which the main conveyor chain is moving. After a slower task is completed, the workpiece is routed back to the main conveyor via a merge module. A slower assembly task may also be performed by removing the workpiece and pallet from the conveyor, performing the task, and returning the workpiece and pallet to the conveyor for transport to the next workstation.
An important consideration in the speed and efficiency of a manufacturing process line using pallets, conveyors, and multiple workstations, is the need for modifying and adapting one or more workstations to perform different operations on different parts. Depending on the product being assembled, a specific workstation will employ one or more of a variety of different assembly devices, including parts pickers, parts feeders and robots. These assembly devices, in turn, require different support and control sub-systems located at or on the workstation chassis, including mechanical mounting systems, electrical controls, pneumatic valves and controls, and computer controls.
Preferably, a workstation chassis used in a pallet-type production line would be designed to support and control a variety of such assembly devices and to allow for rapid changeover to a different configuration without significant disruption of the production process. The chassis would be modular so that multiple chassis can be coupled together using non-synchronous pallet conveyors. The chassis would have its own pallet indexing device so that multiple pallets and workpieces can be accurately positioned at different workstations on the chassis for performing high-speed synchronous assembly operations. Unfortunately, there is no workstation chassis in the prior art that combines modularity, adaptability, speed and accuracy to create a high-speed production line
One object of the present invention is to provide a workstation chassis for a pallet-type automated production line that can be linked together in modular fashion using non-synchronous pallet conveyors.
Another object of the invention is to improve the ability to quickly adapt a workstation chassis to a support variety of different manufacturing process devices.
A further object of the invention is to include multiple workstations on single chassis so that synchronous operations can be accurately performed on multiple workpieces.
These and other objects are achieved by a modular chassis for use in a manufacturing process line wherein manufacturing process steps are performed by manufacturing devices on workpieces carried by pallets. The chassis base supports a horizontal top plate that is machined and tooled for mechanically attaching one or more different types of manufacturing devices to the chassis, such as a robot or automatic parts feeder. An incoming pallet conveyor is aligned horizontally on the top plate to receive a set of incoming pallets from an incoming side of the chassis.
A pallet transfer and indexing module is attached to the chassis proximate the incoming pallet conveyor and is aligned to accept the set of incoming pallets from the incoming pallet conveyor. The pallet transfer and indexing module includes an indexing mechanism to accurately position each of the retrieved incoming pallets in the set in one of a plurality of linearly aligned workstations during a transfer cycle so that at the end of the transfer cycle the process steps can be performed on each of the workpieces supported by each of the plurality of pallets in the set during a process cycle.
An outgoing pallet conveyor is also aligned horizontally on the top plate to receive the set of pallets from the pallet transfer and indexing device and move the set of pallets to an outgoing side of the chassis at the end of the process cycle. A pallet return conveyor is aligned on the top plate parallel to the incoming and outgoing pallet conveyors proximate an operator side of the chassis. Thus, the return conveyor is positioned to receive pallets from other stations on the outgoing side and move them to the incoming side for return to the process starting position.
The chassis further includes at least one power and control sub-system for providing operational power to, and control of, one or more of the manufacturing devices that are attachable to the chassis, and a process control panel viewable from the operator side of the chassis.
A chassis guard is attached to chassis to shield an operator from the manufacturing devices and transfer and indexing module during the transfer and process cycles.
In one embodiment, the modular chassis uses a six workstation indexing operation that allows a complete or partial process to be completed in a high-speed synchronous operation. Coupling multiple chassis together using a non-synchronous link (pallet conveyor) establishes an efficient but high-speed production system. A chassis can be removed from the process and replaced with another to alter the process, or to changeover to another product. A chassis can be re-tooled off line to avoid interference with production.
To provide improved adaptability, the chassis is equipped with electrical controls, pneumatic valves, and mounting holes to allow the user to quickly mount manufacturing devices such as robots or parts feeders for rapid deployment in production. A basic program in an industrial control computer allows easy adaptation to standard assembly or manufacturing operations.
For increased speed of operation, a cam driven indexer moves and locates the pallets a specific transfer distance in the minimum amount of time. A modified sine curve on the transfer cam allows the maximum speed for pallet transfer.
The pre-loaded cam drive accomplishes the pallet transfer in a repeatable accuracy of one thousandth of an inch every cycle. This allows very precise assembly operations to be performed in the pallet fixturing without removing the parts from the pallet.